Self-directed IRAs allow you to invest in a whole lot more than traditional broker-managed IRAs, but there are a handful of things that are not allowed — some for obvious reasons. There are three main categories of what the IRS refers to as “prohibited transactions,” and two of them are fairly straightforward. The last category might need some explaining and examples, because it has to do with your relationship to the person or entity you’re investing in.

Knowing what you cannot purchase with your self-directed accounts is just as important as knowing what you can, because a prohibited transaction — made even unintentionally — could cause your account to lose its tax-protected status.

Without further ado, here’s what you must avoid:

Life insurance. You can’t buy life insurance with your SDIRA. Because life insurance doesn’t grow (policies are for a fixed amount) and doesn’t give returns, it doesn’t fit the way IRAs are supposed to work and therefore doesn’t qualify as an investment. Also, life insurance isn’t even for the plan holder — it’s for their beneficiaries.

Collectibles, like art, antiques, booze, and yes, your great-uncle’s priceless stamp collection. This is fairly straightforward, but in case you’re not sure what could count as a collectible, here’s the IRS’s summary on the topic and some FAQs.

Transactions with disqualified persons. This one can get tricky, but in a nutshell, any kind of “self-dealing” activities are restricted. You, your immediate family members, and any entities in which they own a 50% or more stake cannot directly or indirectly benefit from the investment. There’s a good visual here on who in your family counts as a disqualified person.

Obvious no-nos are that you can’t buy shares in your own company, and you can’t loan money to yourself. A not-so-obvious case, let’s say in a real estate investment, is that you can’t earn income on a house that your adult daughter lives in, even if an unrelated person is paying rent. What about your girlfriend’s mom, who, at some point after the transaction, became your mother-in-law? It’s not as clear cut, and it’s why you should always consult your financial advisor about your intentions to make sure you’re in the clear.

Also on the list of potential conflicts of interest: You also may not invest with a fiduciary or a person who services your IRA, or someone who holds a high position within an entity and earns 10% or more of its profits. “Stepped transactions” to try to get around any of these rules are also prohibited, because they will be viewed as a whole for whatever end you’re trying to achieve (see “Trying to Get Around the Rules” here).

What happens if you make a prohibited transaction accidentally? Well, intentional or not, the penalties for doing so can be pretty steep. For one thing, the year the prohibited transaction is made is the year those assets are considered “distributed” — meaning you have to pay the taxes on them — and the assets are added to your normally taxed income for the year, potentially pushing you into a higher tax bracket. But on top of that, if you’re not over retirement age (59 ½), the IRS also levies a 10% early distribution penalty. Ouch.

The moral here is to just be aware, and when in doubt, talk to your financial advisor before doing anything. Happy investing.

These articles are not intended as investment or financial advice. Before making any investment decision, talk to your financial, tax, or legal advisers.